Radiologist: Diagnoses and treats diseases of human body, using x-ray and radioactive substances: Examines internal structures and functions of organ systems, making diagnoses after correlation of x-ray findings with other examinations and tests. Treats benign and malignant internal and external growths by exposure to radiation from x-rays, high energy sources, and natural and manmade radioisotopes directed at or implanted in affected areas of body. Administers radiopaque substances by injection, orally, or as enemas to render internal structures and organs visible on x-ray films or fluoroscopic screens. May also specialize in diagnostic radiology or radiation oncology. May also diagnose and treat diseases of human body, using radioactive substances, and be certified in Nuclear Radiology or Nuclear Medicine.